Electric impulse lamp as transmitter for light-flash signaling system



June 5, 1956 LIGHT-FLASH SIGNALING SYSTEM 2 Sheets-Sheet 1 Filed Dec. 12, 1952 a R 6 m m m M W i 1 5341 3 m Q a m l K w 4 a I Y W I B e 3 I l/ I 3 A V 3 FD); 5 \AL LI .1

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June 5, 1956 F. FRUENGEL ELECTRIC IMPULSE LAMP AS TRANSMITTER FOR LIGHT-FLASH SIGNALING SYSTEM 2 Sheets-Sheet 2 Filed Dec.. 12; 1952 m m m m United States Patent ELECTRIC IMPULSE LAD/1P AS TRANSMITTER FOR LIGHT-FLASH SEGNALING' SYSTEM Frank Frueugel, Hamburg-Rissen, Germany Application December 12, 1952, Serial .No. 325,512

Claims priority, application Germany January 2, 1552 5 Claims. (Cl. 315-241) The present invention relates to a signal transmitter in the form of a light-flash lamp converting current. impulses into light flashes which are projected by a reflector and received by a light-flash receiver as described and claimed in my companion application, SerialNo. 325,511, filed December 12, 1952, titled Receiver for Light-Flash Signaling System. The signaling system referred .to belongs in the field of optical signaling methods suitable for communication at relatively short distances between moving stations anywhere, but is especially intendcd'for the purpose of increasing safety in road and streettraflic by providing participating vehicles, especially motor cars, with impulse flash lamps and with suitable receivers responding to such flashes, and thus to serve. as overtake signal system in that it enables cars to signal and thereb caution a preceding car before overtaking.

It is one object of the present invention to provide a transmitter for a signaling system of above type which isreIiable inservice, cheap to manufacture and. capable to transmit light flashes which are different than alllight effects otherwise happening in traffic or occurring in nature.

The light flashes emitted by the transmitter in. accordance with this invention have spark discharge character or are spark discharge flashes, i. e., they are produced by electric spark discharges. The term spark discharge character as. used throughout this specificationand the claims is intended to clearly define light flashes having each one the extremely short duration between and 10* second and a steep-fronted wave shape giving rise to a momentary increase in luminous fluxat a rate of more than 10 lumens per microsecond. Therefore, means made particularly sensitive for reception of light flashes thus characterized can be readily protected so they are not disturbed by other light occurrences. Owing to this feature, the spark discharge light flashes are exceedingly well suited to form the fundamentals for light flash signaling, both during day and night time. In addition, the impulse lamp according to this inventionemits light flashes produced by electric spark discharges: which have pronounced light components in the blue and violet spectral region for which the communicating receiver can be made especially responsive.

For transmitting a signal according to this invention, it is possible to project from the car in rear either one: or several spark discharge flashes toward the preceding car which one intends to overtake. The number of flashes necessary to transmit for a reliable warning depends primarily on sensitivity and responsive action of the receiver to which the signal is communicated.

To enhance the reliability of the present device-to the utmost and for this reason to exclude particularly disturbances which could be inflicted by strange light eflects, such as heat lightning near the car, sparking at tramway take-offs, and actual lightning flashes during thunder storms, the present invention in a specific example contemplates to utilize two or more flashes in rapidsuccession and to dimension these flashes either in their duraone or several indicating lamps.

tion and/or their luminous flux gradient so that they are not simulated by the above mentioned occurrences and thus can not be disturbed thereby, provided the receiver is tuned for receiving only such properly dimensioned light flashes. 5

For carrying the invention into effect, it would suffice to operate with single flashes, it has been, however, discovered by this invention that it is advisable to transmit a whole series of stroboscopic light flashes successively at predetermined time spacing and to convert the incident light of these flashes in the receiver into readily perceptible signals by actuating acoustic means or by lighting In the latter case it is thereby preferable to provide also a back-signaling lamp so that the driver of the overtaking car can recognize whether his signal has been received and broughtto-attention. Further details concerning the receiver are disclosed in'my aforesaid companion application.

In order to obviate glare which could be produced if the light flashes of the present signaling. system were too bright, this invention provides that one or a series of spark dischargelight flashes of relatively low intensity, i. e., of lowenergy content, are employed for each signal giving. Such mode of operation has not only the advantage that the flashes, particularly during night time, do not disturb or annoy thecars in counter-traflic, but also that electrical energy is saved.

Asone practical means for-carrying the invention into efiect it has been found possible to employ as spark discharge light source a spark gap that gives sparks or flashespossessing the advantageous characteristics previously referred to, or a spark gap that must be modified inv order to comply with the requirements. The term spark gap md spark as used in this specification implies means for spark-over in the form of a pure spark between electrodes in a gaseous atmosphere including air, but no other type of discharge such as a glow discharge orv are. A spark gap pre-eminently suitable for the purpose of this invention is a gap so proportioned that in it a spark can develop whose resistance approaches the critical resistance in a condenser discharge circuit forming a. series circuit; of resistance, inductance, and capacitance; and in which the capacitance is in the condenser, the inductance in the connections, and the resistance chiefly in: the spark itself. The: fundamental principles of designing such a circuit, which may be termed a controlled spark gap, have been disclosed and claimed in my copending patent application Serial No. 275,157, filed March 6, 1952, for Discharge Device and Circuit for Stroboscopy, to which reference may be had for further details. However, the sparkgap there described is not the only type of spark gap that can be employed for practicing the present invention, and spark gaps of other construction, which fulfill the requirements as previously pointed out, can also be used to good advantage. In designing a discharge circuit for a spark gap in accordance with this invention, it is essential to select conducting means between condenser. and spark gap which have a total inductance lower than 0.2 microhenry. Furthermore, shape and arrangement. of the electrodes forming the spark gap must be such. that the least obstruction. to the emanating light rays of thespark will be caused.

The practical construction. of the present invention. can take several. forms. Generally, the electric impulse lamp is connected to the storage battery of the car and can be switched on. or off by. a switch or push button inserted in the connection and arranged within convenient reach of the driver. In the lamp itself the battery current is interrupted into impulses by a self-interrupter relay and these impulses become efl'ective in the primary of a transformer or secondary-type induction coil. The highvoltage impulses induced in the secondary of the induc- .tionally used on vehicles or the like.

tion coil at the instant of interruption of the primary circuit are applied to charge a condenser which on the other side is connected to a discharge circuit that includes a spark gap. The spark gap is preferably enclosed in a chamber filled with precious gas and is designed for a certain breakdown voltage, preferably in the range of 1,000 to 15,000 volts. This breakdown voltage is somewhat lower than the peak of the voltage impulse imparted to the condenser by the induction coil so that a spark discharge occurs at each instant a voltage impulse is released. The condenser is thereby placed as near as possible to the spark gap in order to reduce the inductance of the discharge circuit as much as possible and thus to obtain a spark discharge of shortest duration, which duration is preferably less than l second, and can be made that short when the constants of the discharge circuit are related in accordance with the principles laid down in my above mentioned patent application Serial No. 275,157.

In accordance with this invention, the spark gap itself can be arranged in a Searchlight-shaped auxiliary unit having a suitable reflector or mirror which can be completely illuminated by the impinging luminous flux eminating from the occurring sparks, whereby it is preferable to give the mirror, coacting with the spark gap, a parabolic shape. In another embodiment according to this invention, a combination of spark gap and mirror is arranged in another light source of such type as conven- If, in accordance with this invention, the spark gap with mirror is arranged .within another light source, for instance, Within the headlamp of a motor car, it is preferable to make the size of this spark-gap-and-mirror unit relatively small in comparison to the size of the reflector of the headlamp in order that the purpose and the efficiency of the headlamp is in no way impaired. In accordance with this invention, similarly good results can be obtained when the said combination of spark gap and mirror is directly incorporated in the headlamp of a motor car. Such a modification of the invention allows numerous different constructions. For equipping already existing headlamps with spark gap and appertaining mirror without having to effect considerable structural changes, it is, in accordance with this invention, possible to build spark gap and mirror as a structural unit and insert it as such into the headlamp of an automobile. In a slight modification of the arrangement just referred to, the mirror of the main lamp (headlamp) itself may take a suitable configuration by having a. small spherical-shaped cavity in which the spark gap is centered, and thus the cavity serves as mirror for the spark gap saving the use of a separate mirror. When so utilizing the reflecting mirror of the main lamp simultaneously as mirror for the spark gap, it is advisable to located the latter adjacent to the light source of the main lamp in order to achieve sufficiently focused spark light emission.

Furthermore, in accordance with this invention, it is possible to combine the light source of the main lamp, for instance, of the automobile headlamp, with the spark gap to one unit, preferably in such a way that the glass envelope containing the lamp filament receives the spark gap too. For example, if a two-filament bulb is used in a headlamp, it is without difliculty possible to shape the antiglare bafile of one filament so that it takes at the same time the place of one electrode of the spark gap. In case the pressure of the gas filling within the bulb of the incandescent lamp should not suffice for satisfying spark emission as prescribed by this invention, it is possible to improve the condition by reducing the inductance of the spark gap circuit and by employing a condenser having a larger capacitance and being operated at a lower charging voltage. As generally known, double filament bulbs are normally filled with precious gas, such as krypton or xenon, in order to prevent condensation of metal vapors on their walls. As similar gases are beneficial for increasing the light yield of a spark gap in accordance with this invention, the gas filling in such bulbs, containing filament and spark gap, serves then a double purpose. In agreement with the provisions of this invention, it is also possible to arrange a spark gap within any common incandescent light bulb and by so doing shape the filament holder so that it can serve as one of the electrodes of the spark gap. If such a combination or dual-purpose bulb is applied in an auxiliary spotlight of a motor car, it can be so switched that the incandescent light is automatically extinguished whenever the fiashing light of the spark gap takes action. Switch-over means of any generally known type can be used for this purpose. Auxiliary spotlights with bulbs containing filament and spark gap, as provided by this invention, have preferably registering means assuring that at least in one position of the spotlight it is definitely certain that the light projected from the spark gap is directed toward the portion of the preceding car where the receiver is located.

In designing a discharge circuit in accordance with this invention, it is advisable to incorporate a condenser having a relatively small dielectric phase angle, especially at high frequencies. It has been found that a very suitable condenser is one wound with layers of a thin plastics foil such as poly-styrene film known as Styrofiex. Furthermore, care has to be taken that the electromagnetic field of the discharge circuit remains relatively small in order to prevent shedding of loss-causing magnetic vectors. To reach this aim it may be desirable to use principally or exclusively ribbon-type cables or leads as circuit connections, whereby, in accordance with another object of this invention, supports of the spark gap itself may serve as current carriers. Moreover, instead of using a single discharge condenser, the necessary capacitance can be accommodated in several partial condensers to good advantage. This depends entirely on the design of the spark gap and its elements.

For a certain transition period during which not yet every motor vehicle is equipped with a receiver for spark signaling, it may be appropriate to combine the spark gap with the acoustical signaling device (electric horn) and this so that both are switched on or off together. Here again this invention provides that component parts of horn and of spark gap can be jointly used. A useful source of energy for the condenser charges necessary for effecting spark operation is, for instance, the magnet of the vibrator to be found in the electric horn of every automobile. This invention provides as another of its features, for bridging the condenser of the spark discharge light source across the vibratory interrupter of the horn and thus use the energy, which would be spilt in sparking at the contacts when blowing the horn, for charging the condenser; or it provides for arranging on this magnet a secondary winding from which high-voltage impulses for condenser charging may be taken.

A device according to this invention serves well not only as an overtake signaling means but also as a warning means well suited to enhance safety at crossroads. In accordance with this invention, such warning feature can be obtained when equipping a stationary trafiic light at the crossroad with an extra lamp, say of yellow color, and connect this lamp in the output circuit of a spark discharge flash receiver mounted in the column of the traffic light so that its phototube can be reached by impinging signals. If now an approaching car actuates its impulse lamp, it is apparent that the extra lamp at the crossing will start to flicker and thus warn another car which may approach on the other road.

From that what has been aforesaid it will become apparent that the present invention can take several forms in its arrangement, in its construction, and in its application; and the now following description of some preferred embodiments will serve to convey a better understanding of some advantages and novel features, but is .ductance in the condenser discharge circuit.

in no way to be construed as limiting to. the scope of. this invention as claimed in the appended claims.

In the: accompanying drawings, which show diagrammatically these preferred embodiments,

Fig. 1 illustrates a longitudinal section through an impulse lamp constructed as an auxiliary accessory for an automobile;

Fig. 2 is an electric circuit diagram of the lamp shown in Fig. 1;

Fig. 3 illustrates the construction of an induction coil with a condenser as surface layer thereof, a unit as preferably used in connection with impulse lamps of this invention;

Fig. 4 is a simplified representation of. a. spark gap with its mirror;

Fig. 5 shows a spark. gap unit. as indicated in Fig. 4 arranged in a reflector of an automobile headlamp;

Fig; 6 shows a spark gap unit of. somewhat modified form inserted in a socket provided in the reflector of a headlamp;

Fig. 7 illustrates a spark gap without own mirror, inserted in a socket provided in a headlamp reflector which has been shaped to form a reflecting cavity for the spark p;

Fig. 8 is a double-filament lamp bulb having a spark gap incorporated in its envelope; and

Fig. 9 is a single filament bulb having aspark gap within itsv envelope.

Referring to Fig. 1, there can be seen the spark gap enclosed within a sealed glass envelope 1. However, it is to be understood that adequate service can in some instances be had from a spark gap in open atmosphere. The enclosed spark gap as shown can be in the form of a commercial projector lamp having suitable electrodes and a filling of precious gas, for instance, argon. Such sealed lamp 1 is arranged at the center of a parabolic reflector 2 so that the spark gap coincides with the focal point of the parabola. A lens in front of the lamp causesv spreading of the emanating light beam for about 10 to degrees. Immediately adjacent to the contacts of the sealed lamp 1 and behind the reflector 2 there are arranged one or several storage condensers 3, which in the illustrated embodiment comprise two disk-type ceramic capacitors having a capacitance. in the range of 10 to 10 micromicrofarad. This arrangement of the condensers adjacent to the contacts of the lamp body is very essential for obtaining the lowest possible in- Thisinductance should preferably be much lower than 1.0 henry in order to achieve discharge flashes of a durationwithin the range of $5 microsecond; flashes which normally do not occur in nature and for which the receiver to communicate with this impulse lamp as transmitter isespecially attuned. Computations being necessary for arriving. at most favorable circuit constants for a dischargev circuit by approaching the aperiodic limit or, in other words, by approaching the critical case in such circuit, being a series circuit of resistance, inductance and capacitance, are outlined in my aforementioned copending application to which reference may be made for further details. Within the space between parabolic reflector 2 and the Searchlight-shaped housing 7 of the complete impulse lamp, there are accommodated the automatic circuit interrupter 5, a spark absorbing and interference suppressing condenser 6, and a transformer 4 in the form of an ignition coil or the like. The latter is necessary for transforming low voltage, usually derived from a storage battery, into a suitable high-voltage for charging condensers 3. A suitable bracket 8, secured to housing 7, serves for fastening the impulse lamp to a support on the motor car and permits tilting into suitable inclination in the direction of travel. A terminal screw is indicated at 9, which serves for connecting the lamp to the, positive terminal of the storage battery (not shown) by'way of a switch 10 placed for convenient actuation bythe driver of the car. The negative terminal of the lamp circuit is internally connected to housing 7 and thus in contact with the chassis of the car.

In the circuit diagram shown in Fig. 2, the several circuit elements are designated by the similar reference numerals as in Fig. 1, and all connections can thus. be readily ascertained.

The impulse lamp, generally constructed as above descirbed, must be dimensioned according to certain rules when satisfying performance in connection with a storage battery is desired. The starting point for proper designing is the energy desirable to convert in the fiash. Let this energy be joule in an example now to be given for clearer understanding. The discharge chamber, preferably in the form of a small sealed projector lamp, may be designed for a breakdown voltage of 5 kilovolts. The discharge condenser necessary for feeding such a spark gap has, according to the fundamental energy formula, an energy content of W= /2 C. E joules (C=condenser capacitance in microfarad, E=voltage in volts). Solving for C gives C=2 W/E and inserting the values of the present example gives =8,000 micromicrofarads.

Charging of the condenser in the present case is effected by opening the primary of transformer, or secondary type induction coil 4, and thus releasing the energy stored in the magnetic core through the secondary into the con denser which is connected. thereto. The amount of magnetic energy invested in the core by the battery through said primary must be higher than A joule, say, for instance, /5 joule. Consequently, by assuming that a common ignition coil having an inductance of about. henry is used, the primary current becomes, when correspondingly solving the fundamental formula W /2 LI (L==inductance in henry, l=current in ampere),

T 2 amperes The primary winding of the induction coil must therefore be wound with a wire of such cross-section that at least 2 amperes will flow at the prevailing voltage, which as such can be arbitrarily chosen and is preferably the voltage of the battery. In order to obtain insensitivity to voltage fluctuations and to protect the coil against excessive currents, it is advisable to apply the principle of the self-interrupter-type relay in such a manner that the relay contacts automatically interrupt the circuit when the current in the primary coil, which is simultaneously the energizing Winding of the relay, has reached about 2 amperes. The interruption of the primary circuit causes then an impulse in the secondary circuit which is high enough to effect breakdown of the spark gap and flashing. With the primary circuit interrupted, the tractive force of the core ceases and the contacts return again into their natural closed position, whereupon the cycle is repeated anew. The amount of secondary energy in the discharge circuit is independent of dimension and size of the charging induction coil, because breakdown of the spark gap within the dscharge chamber occurs only at a given voltage Which is characteristic for a certain gap and in the present case, it will be remembered, is 5 kilovolts. By assuming a discharge circuit inductance of 0.03 microhenry, a value so low that it is practically not attainable, it is possible to calculate the maximum discharge current when neglecting the spark resistance and applying the following equation: LsXI .s=csXE s where LS isthe Cs is the capitance (in the present example 8,000 micromicrofarad), and Es is the charging voltage (here 5,000

1 7 volts). By inserting the values and solving for Is, it

becomes Thus the momentary peak energy released in the dis charge circuit may be calculated to be at an average or 6.25 megawatts. Assuming an efiiciency of per cent in the light flash, the light energy becomes about 300 kilowatts and rises to this peak value within a duration t= /L; Cs=abt. 2 l0 second.

For close distances or when working in conjunction with very sensitive receivers, it suflices generally to employ very low condenser capacitances or to depend partly or mostly on the capacitance inherent in the connecting conductors, which may be as high as 10 to 100 micromicrofarad. Moreover, it is possible to employ a special construction of an induction coil as shown in Fig. 3, into which a certain capacitance has been incorporated. Such a capacitor may consist of two metal foils 11 wound as layers of the coil itself. One of the two foils 11 is to be grounded to the lamp body and the other connected to the high-voltage side of the circuit. An insulating tape 12 known under the trade name Triacetate Foil has been found very suitable to serve as insulating material between the metal foils. For the purpose of reducing the inductance of the discharge circuit as much as ever possible, it has been found to be advantageous to lead one current path through a parabolic reflector itself, which, for reducing the ohmic losses, is silvered on its rear side, or, for sake of simplicity, is silvered all around. Good results can also be obtained with aluminum reflectors. There appears to be no drawback in employing aluminum reflectors with some oxide-protective coating, because the current flows definitely only within the good conducting metal and not at all in the perfectly insulating coating. For insulating the high-voltage carrying socket of the sealed lamp 1 and for protecting the same from humidity influence, it is advisable to use Plexiglas or amber insulation 13 and to apply paraflin or other waterskin-rejecting impregnation. To obtain a connection of very low inductance between condenser and spark gap, a ribbon-type cable having low wave impedance can be used with good success. The parabolic reflector, if utilized as a current carrier, is a perfect equivalent of a conductor of low wave impedance.

watts.

The spark discharge gap in its simplest form need not be sealed in a glass envelope but can be in the form of a common spark plug or other spark gap construction so arranged that the sparks, jumping between the electrodes, occur at the focal point of the lens or the parabolic reflector. desired, it is advisable to enclose the spark gap within a chamber filled with precious gas, preferably with argon, or, if especially high light efliciency is desired, with krypton or xenon. For most eflicient operation, the pressure of the gas filling and the length of the spark gap must be properly related, whereby spark gap lengths between 1 and 10 millimeters, and gas pressures in the range of 0.5 to 10 atmospheres absolute, are workable. Aluminum as material for the electrodes gives by the generally prevailing low average current load very good results. For heavier loads and more frequent service, however, it is better to use fine-granulated sintered tungstenpowder compacts for electrodes, whereby in both cases it is desirable that a low sputtering (evaporating) of electrode material takes place during sparking. Such action will further enhance the radiant light flux of the sparks in the blueand violet spectral region; a region already inherently pronounced in light emitted by electric sparks and comprising light for which the signal receiver of the present system is made to be particularly responsive.

If, however, a higher yield of useful light is In order to be able to adjust the impulse lamp of this invention readily when employed as overtake signal transmitter in road trafiic in spite of its relatively low visual light emission, it is expedient to secure it in conjunction with a convex rear-view mirror as generally used in motor cars, and thus obtain proper adjustment by just setting the rear-view mirror in habitual manner. Another possible means for facilitating adjustment is a suitable interlinkage with the automobile headlamps. Then it is only necessary to properly align the headlamp light beam and the impulse lamp will be automatically set in proper relation therewith.

In an attempt to avoid the necessity of carrying an auxiliary impulse lamp on every car when utilizing the present light-flash signaling system, the present invention in another of its embodiments provides a relatively small spark gap unit (Fig. 4) comprising a spark gap 15 enclosed in a sealed envelope and resembling a small light bulb itself, a base 16, and a mirror 17. The lead of one electrode extends through the base, the other electrode is sealed in the free end of the envelope and connects to leads 18 which at the same time serve as bracings for the spark gap. Such a spark gap unit is then mounted within the parabolic reflector 19 with light bulb 20 of an automobile headlamp as indicated in Fig 5. The leads of the spark gap are preferably extended through holes in reflector 19 and the condenser 3 is secured directly behind the reflector to obtain a discharge circuit of low inductance. The induction coil and interrupter can be placed away from the discharge circuit at another convenient place in the car. A neater mounting can be had if the reflector of the headlamp is provided with a socket 35 as indicated in Fig. 6. The small parabolic mirror with which the spark gap itself is equipped can be eliminated when a certain portion of the reflector of the headlamp is shaped to form a cavity as indicated at 21 in Fig. 7. This cavity is designed to project the light of spark gap 15, inserted in socket 35, in the desired direction.

Instead of arranging the spark gap as a separate unit within the area of a headlamp reflector, it is also possible to incorporate the spark gap in the light bulb of a luminaire. The Fig. 8 shows such a construction in which a two-filament lamp is provided with a spark gap 15. The two filaments are indicated at 22 and 23, and the antiglare baffle 24 is constructed so that it simultaneously serves as carrier for one electrode 25. The other electrode 26 may be sealed in the glass envelope and have a lead 27 attached thereto, or it may be carried by a holder 28 (indicated in dotted lines) inside the bulb, which holder serves also as current lead to electrode 26. The Fig. 9 shows a simple construction of a single filament light bulb in which a spark gap has been incorporated by letting one holder 29 of the filament 30 form also one electrode 31 of the spark gap, whereas the other electrode 37 is formed at the tip of another suitably shaped holder 33 joined to an additional lead-in wire. Such dualpurpose lamp bulbs as shown in Figs. 8 and 9 have an additional terminal for introducing the high-voltage impulses to the separate spark gap electrode, the other electrode, joined to the filament, has its terminal in common with one of the filament terminals.

In operating the dual-purpose lamps just described, it has been found that the peak intensity of the spark-over is minimized by the incandescence of the lamp filament. This phenomenon is due to the fact that the electrons liberated from the filament are negatively charged and increase the conductance across the spark gap, thus hampering the creation of a high potential and the etficacy of the spark-overs. The drawback just mentioned can be overcome when, according to this invention, the separate electrode, i. e., the electrode not joined to the filament, is made the negative electrode in the discharge circuit.

. Since thus the electrons participating in the spark discharge must move in opposite direction to the electron flow of the filament, the development of the full break- 9 down potential at the spark gap and the intensity of the spark cannot be impaired by the incandescence of the filament.

During prolonged service of incandescent lamps containing a spark gap it could be noticed that the luminous flux emission of the filament decreased in time on account of particles sputtered from the spark gap electrode by metal evaporation, which particles settled on the filament. In order to prevent such affection, this invention contemplates to make the electrodes of the spark gap from a material akin to the material of the filament. It has been found that tungsten, tantalum, or, to a lesser degree, also molybdenum are materials which can be used without affecting the life of the lamp filament. Since filaments are generally made of tungsten, it will be obvious that tungsten particles settling on the filaments will not diminish their light emission.

The arrangement of the light bulbs in automobile headlamps is generally at the focal point of the reflecting mirror so that the emanating light beam lights up an area in front of the traveling car as is most suitable for safe driving. Entirely different requirements govern the direction of the light flashes projected from the spark gap. These must be in a direction assuring that a maximum of their eifective light reaches the pickup lens of the receiver on the car in front. According to this invention, it has been found most suitable to equip the left-hand headlamp with a dual-purpose bulb containing the spark gap, and to locate the spark gap therein so that the reflector projects the flashing light beam preeminently toward the left side of the street and in somewhat upward slanting direction. Proper location of the gap within the bulb can readily be obtained by suitably forming the electrodes and their holders.

When speaking of light flashes in this specification and particularly in the claims, this expression is intended to be interpreted as including also flashes of light in the ultrared and ultra-violet spectral region. Furthermore, when referring to condenser in the claims, that what is meant is a condenser unit which may be a single condenser or a group of parallel-connected condensers; and the term gaseous atmosphere is intended to include also air as generally defined. Although the invention has been described in detail in connection with a few preferred embodiments, it will be understood that further modifications will occur to those skilled in the art, and that all such changes must be considered to fall rightfully within the scope and spirit of this invention.

What I claim is:

1. In an electric impulse lamp for light flash signaling the combination, with an incandescent lamp, of a pair of electrodes forming a spark gap, a filament, an envelope enclosing said spark gap and filament, and a gaseous filling within said envelope.

2. In an electric impulse lamp for light flash signaling the combination, with an incandescent lamp, of a pair of electrodes forming a spark gap, a filament, an envelope enclosing said spark gap and filament, a holder for said filament, said holder being shaped to form simultaneously one of said electrodes, one common terminal for said filament and said electrode, a separate holder for the other of said electrodes, one terminal for the other end of said filament, one terminal for the other of said electrodes, a storage condenser connected between said common terminal and said electrode terminal to form in combination with said pair of electrodes a condenser discharge circuit across said spark gap.

3. The structure of claim 2 in which control means are incorporated for releasing discharge impulses from said condenser across said spark gap in such a direction that the separate electrode becomes the negative electrode.

4. The structure of claim 2 in which said pair of electrodes consists of a material akin to the material from which said filament is made.

5. The structure of claim 2 in which a parabolic reflector is incorporated so that said filament lies substantially at the focal point of said reflector, whereas the spark gap is located so that the beam of light emanating from it is projected preeminently toward one side and slightly upward.

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